Adhesive compositions and process



Patented Mar. 18, 1947 I 2,411,792 annssrvs COMPOSITIONS AND PROCESS John J. Verbanc, Tuxedo Park, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application August 19, 1943,

Serial No. 499,229

7 Claims. (Cl. 260-768) This invention relates to an improved composition of matter and a method of making the same. More particularly, the invention pertains to an improved adhesive composition which is adapted for use in bonding natural and synthetic textile fibers and especially rayon to various elastomeric materials.

The fact that viscose rayon is not wet" by rubber and rubber-like materials, and consequently, when composite. articles, for example tire carcasses, are made from viscose rayon and rubber or a rubber substitute, only a very slight adhesive bond exists between the fabric and the rubber, has long been recognized as a major detriment to. the commercial use of this valuable synthetic fiber. A large number of. methods have previously been proposed to develop adhesion between rayon and rubber, one of the most successful of which consisted in the use of a latex-resorcinol-formaldehyde treatment. However, this type of adhesive has many inherent deficiencies. For example, it discolors and decreases the flexi-- bility of fabric. The coating is rigid and brittle and therefore is easily damaged by handling. The composition consisting of latex and a resorcinol formaldehyde resin must be used immediately, since on standing it gels to an unusable condition. In addition, this method involves the use of an aqueous solution which is very harmful to the rayon fabric and requires long periods of drying at elevated temperatures, which in turn, decreases the possible output of treated fabric from equipment of definite size.

An object of this invention, therefore, is to provide an improved adhesive composition which I tenaciously adheres textile fibers, and especially fibers of viscose rayon, to vulcanized rubber and rubber-like substances. A further object is to provide an adhesive composition which when placed on a textile fabric will not excessively discolor or stiffen the fabric. In addition, it is an object of this invention to provide an adhesive composition which will bond textiles to rubber and its substitutes at normal and at elevated temperatures. e. g., from 25-l25 C. It is also an object of this invention to produce an adhesive composition which will produce adhesive bonds between textile fibers and vulcanized rubber or rubberlike substances which will remain efiective at elevated temperatures in the presence of water. A further object is to provide an adhesive from rubber and a polyfunctional isocyanate compound which will remain stable and usable as an adhesive for a period of several months. These and further objects will appear hereinafter.

These objects are accomplished by the present invention which, briefly stated, comprises treating isoprene polymers dissolved in a, solvent with an organic polyisocyanate compound and heating the resulting cement. The heating is carried out until a large drop (e. g., as high as a 20-30% decrease or more) in the viscosity of the cement is noted.

This reaction can be hastened by premasticating the isoprene polymer in the presence or absence of rubber peptizing agents, e. g., aromatic mercaptans. The reaction may also be hastened by the addition of rubber peptizing agents directly to the cement prior to heating.

By the term isoprene polymer I mean to include both natural rubber, e. g., smoked sheets, pale crepe, gutta percha and balata, and also synthetic elastomers prepared by polymerizing isoprene.

Throughout the description of this invention the term plasticity is employed to quantitatively describe the state of the isoprene polymer, e. g., rubber, being used. The numerical index in the term refers to the thickness in thousandths of an inch obtained when a pellet 2 cc. in volume is compressed isothermally at C. between platens of a press loaded with a weight of 5000 grams for a period of three minutes. The term used is an inverse measurement of softness; i. e., -plasticity rubber is not as soft as 60-plasticity rubber.

The term "elastomeric material as used herein is intended to cover natural rubber, for example, smoked sheets, pale crepe, gutta percha and balata, and also various synthetic rubber-like materials produced from such materials as isoprene, butadiene, chloroprene, etc., alone and with other polymerizable materials. As examples of these may be cited the neoprenes, Hycar, Chemigum, GR-S. Buna S, Buna N, Perbunan, and rubber.

The following examples further illustrate the principles of my invention and divers embodiments including the best mode contemplated for carrying out the same. Parts are given by weight throughout the specification unless otherwise indicated.

EXAMPLE I 50 parts of blended smoked sheet rubber and 450 parts of dry xylene were charged into a stainless steel kettle. 0.25 part of thio-alpha-naphthol was added with stirring and the contents of the kettle heated at C. for a period of 48 hours. 10 parts of methylene-bis-(4-phenyl-isocyanate) was added and the cement heated for an additional 24 hours. The reaction mixture was cooled and discharged from the kettle. 492 parts of a smooth cement was obtained (96% of the theoretical yield). The product obtained had a specific gravity of 0.86 at 25 C. and a Stormer viscosity of 7.5 seconds at 25 C. This material when tested for bonding power as outlined in co-pending Neal and Verbanc application, Serial No. 436,536 filed March 27, 1942, was shown to be an eflicient bonding agent for adhering rayon,

the efilciency of this cement as an adhesive increases as the heating cycle progresses. Although further heating (above 160 hours) decreases the efiectiveness of this cement as an adhesive slightly, the fact that this cement can be heated at elevated temperatures for such a Bonding viscose rayon to an elastomer composition Stonncr viscosity in seconds at 25 C. Deposition alter aging cement Vulcanizaor men ble clastomer caloass stock per cent wei ill. on is ric 12 weeks 1 7.6

. 1 Pounds pull per linear inch at 25 C.

The data listed shows that poor adhesion exists between untreated regenerated cellulose and a rubber or Buna S (butadiene-styrene copolymer) carcass stock. Treatment with the adhesive cement of this invention, however, improves the bond tremendously. The stability of the cement does not change appreciably over a 20 week period as indicated by the viscosity and bonding efficiency.

This cement has also been found to be satisfactory for treating tire cord fabric manufactured from regenerated cellulose. Tires built from such cord have proved to be superior to tires made using either cotton cords or regenerated cellulose cords treated by the conventional resorcinolformaldehyde/latex cement.

EXAMPLE II Rubber cement containing hemamethylene dz'isocyanate, heated at 75 C.

Bonldirluz regenerate Hours Viscosity 5 m Exp. No. healing in sec onds fi at 75 C. at 25 0. 50 mgr deposilion on fabric l Toluene blank-12.2 seconds.

From the data listed in Table II it is apparent that a large decrease in viscosity occurs on heating the cement at 75 C. It is also apparent that long period of time and still remain effective further demonstrates the stability of cements prepared by this invention and the wide limits of the process.

EXAMPLE m 900 parts of dry carbon tetrachloride, 100 parts of unmilled smoked sheet rubber and 1.25 parts of thioalpha-naphthol were placed in a reaction vessel equipped with an agitator, reflux condenser, and a thermometer. The contents were heated at C. for 24 hours. During this period the rubber dissolved forming a smooth cement. 20 parts of methylene-bis-(4-phenyl-isocyanate) was added and the reaction mass heated at 75 C. for an additional 8 hours. The charge was cooled to 25 C. and removed. This cement was tested as an adhesive for bonding regenerated cellulose to vulcanizable elastomer carcass stocks. The results obtained are shown in Table 111.

Teen: Ill

Deposition of cement Pounds pull per linear inch at 26 C.

Bonded to carcass stock fabric) l Neoprene made according to U. S. P. 2,264,173, Example 25.

EXAMPLE IV parts of umnilled pale crepe rubber, 900 parts of dry xylene and 12.5 parts of hexamethylene diisocyanate were placed in a reaction vessel equipped with agitation, a reflux condenser, and a thermometer. The contents of the reaction vessel were heated at C. for a period of 35 hours. During this time a smooth cement was formed, which had a Stormer viscosity at 25 C. of 7.3 seconds. This adhesive was tested as a bonding agent for adhering regenerated cellulose to a vulcanizable carcass stock. The test results are shown in Table IV.

TABLE IV I Bonding regenerated cellulose to a vulcameoble rubber carcass stock Deposition of cement Pounds pull Exp. No. (per cent per linear weight of inch at 25 C.

fabric) 5 Z5 10 26 15 30 20 36 Blank 3. 0

EXAIMPLE V 100 parts of unmilled smoked sheet rubber, 900 parts of dry xylene, 0.1 part of thio-alpha-naphthol were placed in a reaction vessel equipped with a reflux condenser, an agitator and a thermometer. The mixture was heated at 135 C.

for a period of '72 hours, during which time the rubber dissolved to form a low viscosity cement, 20 parts of methylene-bis-(4-phenyl-isocyanate) was added and the heating continued for 24 sion between cotton and rubber. Data obtained is given in Table VII.

TABLE VII hours. The cement was cooled and discharged. 5 Data obtained in bonding regenerated cellulose Bonding 30 cotton belting fabric to to rubber, Buna S-and neoprene are shown in carcass stock Table V.

Deposition Pounds pull TABLE V ofeemcnt per linear 1 Exp. No. (per cent inch Bonding regenerated cellulose to elastomer $3533 3 carcass stocks 10.0 as 15.0 40 Deposition 20. 0 47 of cement Elastomer Pounds pull 25. 0 60 Exp. No. (per' cent carcass, per linear Blank 19 weight of stock inch at 25 C.

fabric) 29 The outstanding strength of the adhesive bond 10 Neoprene L. 25 obtained between 30 oz. cotton belting fabric and a rubber carcass stock by this method is show Blank Neoprene 2.5 by the following test. Blank Square woven 30 oz. cotton duck was painted 1 Neoprene made according to U. S. 1?. 2,264,173, Example 25. This cement was also eiiective in bonding cotton and nylon to rubber carcass stock.

EXAMPLE VI 100 parts of crude smoked sheet rubber, 900 parts H-51 solvent (petroleum fraction B. P.=105-150 C. approximately) and 1 part of thio-alpha-naphthol were placed in a reaction vessel equipped with an agitator, a reflux condenser and a thermometer. The contents were heated at 100 C. for a period of 16 hours. 20 parts of methylene-bis-(4-phenyl-isocyanate) was added and the heating cycle continued for 8 hours. The cement thus obtained was light colored and smooth, and had a Stormer viscosityof 10.3 seconds at 0. Test data obtained in bonding regenerated cellulose to various elastomeric materials both at 25 C. in air and at 70 C. in the presence of water is listed in Table VI.

TABLE VI Bonding regenerated cellulose to vulcanizable elastomer stocks Pounds pull per Deposition E No of cement Elastomer near Inch (per cent stock weight of bonded to- C 7 0 fabric) (air) (H2O) 5.0 Rubber. 15. 0 10. 0 10.0 d0 30.0 23.0 5 0 Neoprene 12.0 6.0 10.0 d0 24.0 14.0 5.0 Buna S- 15.0 11.0 10.0 ..--.d0 27.0 23.0

1 Neoprene made according to U. S. P. 2,264,173, Example 25.

Neoprene made according to U. S. P. 2,264,173, Example 25.

with three coats of the rubber cement of Example VII, drying the treated fabric at 60 C. before each application. After final drying the treated fabric was frictioned on both sides on a calender using the following rubber stock.

Rubber friction stock For constitution see Du Pont Rubber Chemicals-Report No. 43-1, February, 1943.

1 For constitution sec Compounding Ingredients for Rubber-Bill Bros. Publishing Corp., 1936.

Belting was then plied up using alternating layers of frictioned fabric (8" x 8") and rubber carcass stock having a gauge thickness of 0.010".

Rubber carcass stock Rubber.-- 1 Zinc oxide Stcaric acid. Neozonc" D Pine tar 2-mcrcaptobenzothiazole Sulfur r m rse-. 3128388 The final composite article consisted of four plies of frictioned fabric and three plies of rubber carcass stock. The slab was then inserted in a mold (8" x 8" x built up to mold level by additional layers of tin foil and cured 30 minutes at 40# steam pressure. The cured slab was allowed to cool to 28 C. and cut into 1" x 7" test strips.

The test strips were mounted on a U. S. type flexing machine and flexed under a load of employing a speed of cycles/minute and a hub having a, 1.25" O. D. The specimen was considered to have failed when there was a clear separation across the width of the specimen. Flexing data are given in Table VIII.

' moved at the times noted, the teststrips showing no signs of failure.

EXAMPLE VIII 1000 parts of xylene, 100 parts of unmilled smoked sheet rubber and 2.5 parts of thio-alphanaphthol were placed in a reaction vessel equipped with agitation, distilling column and a thermometer. The reaction mass was heated to 141-42 C. and 100 parts of xylene distilled. The distilling column was changed to reflux and 20 parts of methylene-bis-(4-phenyl-isocyanate) was added. The solution was heated 8 hours at 135 C. and the resulting product cooled to 30 C. and discharged. The adhesive was tested as a bonding agent for adhering square woven regenerated cellulose fabric to rubber and Buna S carcass stocks. Deposition of 5% of this cement on the fabric gave a bond with either elastomer which required a pull of 25 lbs. per linear inch for rupture.

EXAMPLEIX 1000 parts of xylene and 100 parts of commercial grade gutta percha were placed in a glass reaction vessel and heated at l4142 C. in order to distill off 100 parts of solvent, thus removing all traces of water from the resulting cement. 20 parts of methylene-bis-(4-phenyl-isocyanate) was added and the mixture heated at 135 C. for a, period of 8 hours. The resulting dark colored cement was smooth and had a low viscosity. This cement was tested as an adhesive for bonding viscose rayon to rubber and Buna S. The results are shown in Table 11!.

TABLE IX 500 parts of xylene, 35 parts of poly-isoprene (prepared by emulsion polymerization of isoprene in an alkaline system) and 0.5 part of thio-alphanaphthol were placed in a. reaction vessel and heated at 141-42 C. with agitation until 180 parts of xylene was distilled oil. This served to remove water from the remaining cement. Seven parts or methylene-bis-(4-phenyl-isocyanate) was added and the cement heated at 135 C. for a period of 8 hours. 356 parts of a smooth cement resulted having a Stormer viscosity of 8.1 seconds. When used as an adhesive for bonding rayon to a rubber carcass stock, a 10.9% coating of this adhesive on the fiber gave a bond strength of 26-28 lbs/linear inch.

It is to be understood, of course, that the above examples are merely illustrative and that the invention comprehends a wide variation in reagents and conditions from those above specifled. Thus, although most of the examples utilize a 10% cement, I have found that the concentration is not critical but may be varied from 1-50% depending upon the plasticity of the rubber used. the solvent employed and the heating time and the deposition required. The preferred range is from 540%.

The amount of the poly-isocyanates in the cement composition may range from 0.5 to by weight, based on the weight of the elastomer, the preferred concentration range being 5 to 25%.

As examples of organic poly-isocyanates the following may be named: hexamethylene diisocyanate, para-phenylene diisocyanate, 2,3-dimethyl-tetramethylene diisocyanate, decamethylene diisocyanate, para,para'-diphenylene diisocyanate, 2-chloro-trimethylene diisocyanate, 5-nitro- 1,3-phenylene diisocyanate, ethylene diisocyanate, dodecamethylene diisocyanate, meta-phenylene diisocyanate; polymethylene diisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, etc.; alkylene diisocyanates such as propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, butylene- 2,3-diisocyanate; cyclo-alkylene diisocyanates such as cyclo-hexylene-1,2-diisooyanate; aromatic diisocyanates, 1-methyl-phenylene-2,4-diisocyanate, naphthylene-l,4-diisocyanate; aliphatic aromatic diisocyanates such as xylene diisocyanate, methylene bis (4-phenyl-isocyanate) and diisocyanates containing hetero atoms such as In fact, any poly-isocyanate of the general formula R(NCO)n in which R is a polyvalent organic radical and n is an integer larger than 1, will function for the above said purposes of the present invention.

Although xylene has been specified in most'oi the above examples as the solvent for the rubber and the cyanate compound, it is to be understood that this invention is not limited thereto and that any liquid which is non-reactive with the cyanate compound, and which is a solvent for both the rubber and the cyanate compound will be suitable, e. g., benzene, gasoline, carbon tetrachloride, ethylene dichloride, chlorobenzene, kerosene, etc., or mixtures thereof.

The temperature at which these cements are heated does not appear to be critical, but can vary between wide limits. In most instances the temperature at which the cement is heated is dependent upon the boiling point of the solvent. However, it is possible to employ a closed vessel which will withstand internal pressure in order to heat a cement above the boiling point of the 9 particular solvent employed. A temperature range of 75-250 C. is generally satisfactory while the preferred range is 75-150 C.

The time of heating can also vary between wide limits. It is directly dependent upon the following factors:

(1) Plasticity of rubber.

(2) Amount of peptizing agent.

(3) Concentration of cement.

(4) Type of solvent employed and its boiling point.

In general, however, the heating period should continue until a large decrease in viscosity of the cement is noted (see Table II). The preferred range, however, is from 1-72 hours.

The amount of peptizing agent may also be used over a large range in concentration. I have found; however, that from 1 to 5% based on the rubber is suflicient. As peptizing agents any of the known peptizing agents for rubber may be used.

The quantity of the adhesive composition of this invention applied to the yarn, cord or fabric to be adhered to the elastomeric material will vary, depending upon the article to be manufactured and the strength of the bond desired; satisfactory results are obtained when the increased weight of the treated yarn, cord or fabric, which measures the quantity of cement applied, is from 0.25% to 95%. In general, amounts of 5% to 20% give very satisfactory results and constitute the preferred range. The yarns, cords or fabrics may be treated with this adhesive combination by any suitable means such as by immersing in a dipping tank, regulating the amount of material adhering to the fabric by means of squeeze rolls, scrapers, or other suitable devices, or by merely allowing the excess to drain off followed by solvent evaporation either spontaneously or at elevated temperatures.

The cord, fabric or other structure bonded by means of this adhesive may be composed of natural cellulosic fibers such as cotton, or of regenerated cellulose produced by the viscose process or regenerated cellulose produced by the cuprammonium process, or cellulose esters and ethers. The cord or other structure may be composed of a plurality of filaments or it may be composed of a monofil.

Cords and fabric made from materials other than cellulosic materials, such as wool and nylon, may also be bonded to vulcanizable elastomeric materials by use of this adhesive. This adhesive is also useful for bonding elastomers to wood, leather, metals and the like.

Several of the more important advantages of my invention are illustrated by the following tests: If square woven viscose sailcloth, treated with the cement of this invention, is placed upon a commercial compounded rubber stock, such as is customarily used in the manufacture of tires, and the whole vulcanized, the treated rayon is found to be strongly bonded to the rubber. If the treated rayon fabric is subjected to a standard pull-off test at an elevated temperature, for example, 212-250 F., to measure the bond between the fabric and elastomer at this temperature, the bond is found to be superior to that of a. cotton fabric to rubber at this temperature, a fact which is of the utmost importance in the construction of tires, fan belts and similar articles, which develop a high temperature under normal conditions of usage. Many of the pre- In direct contrast to adhesive compositions not 1 containing polyisocyanates, the present invention increases the durability of flexing and bending of a pad consisting of plies of fabric treated as outlined above to which a skim coat of compounded rubber stock has been applied and the resulting pad vulcanized. For example. while a, pad prepared from untreated regenerated cellulose fabric may be flexed 2,250 times and a similar one from untreated cotton may be flexed 27,000 times before separation ofgthe plies takes place, a pad prepared from regenerated cellulose fabric treated with the adhesive of this invention may be flexed about 144,000 times before separation of the plies takes place.

In addition to the foregoing advantages, the treatment of regenerated cellulose cord or fabric with cements of the present invention does not excessively discolor, stiffen or harden the cord or fabric. The cordsor fabrics treated with this cement are relatively non-tacky and exhibit no peeling or cracking as is often the case with adhesives known to the art at the present time. The process of treating cellulosic materials as outlined in the examples, contrary to the processes of the prior art, is performed in the absence of water. Water is known to be deleterious to regenerated cellulose cord and fabric, since it causes a pronounced swelling and weakening of this material. This adhesive also possesses several additional advantages. These are: (1) ease of application, (2) simplicity of equipment, making unnecessary any pronounced changes in the equipment in current commercial processes for the treatment of fabrics or individual cords, and (3) the cheapness and availability of these raw materials. First and foremost, however, this invention makes possible the production of adhesive compositions containing rubber and a polyfunctional isocyanate compound which can be stored for long periods of time without loss in either coating or bonding eificiency.

Since it is obvious that various changes and modifications may be made in the above description without departing from the nature or spirit thereof, this invention is not restricted thereto except as set forth in the appended claims.

I claim:

1. An adhesive composition suitable for bonding textile reinforcing structures to elastomeric stock which comprises the reaction product of an organic diisocyanate and an elastic isoprene polymer dissolved in an organic solvent for said reaction product.

2. An adhesive composition suitable for bonding textile reinforcing structures to elastomeric stock which comprises the reaction product of an organic diisocyanate and rubber dissolved in an organic solvent for said reaction product.

3. The reaction product of an organic diisocyanate and an elastic isoprene polymer.

4. The reaction product of an organic diisocyanate and rubber.

5. An organic textile material coated with the reaction product of an organic diisocyanate and an elastic isoprene polymer.

6. The process which comprises reacting a mixture comprising an organic diisocyanate and an elastic isoprene polymer dissolved in an inert organic solvent at a temperature of from 75 to C. for a period of from 1 to 72 hours.

7. The process which comprises reacting an REFERENCES CITED The following references are of record in the file of this patent:

Number 12 UNITED STATES PATENTS Name Date Borough Mar. 24, 1942 Kellog Mar. 16, 1943 Roguemore Aug. 15, 1944 

